Depth motion determination via time-of-flight camera

ABSTRACT

A time-of-flight camera includes a light emitter, a photo detector, and a controller. The time-of-flight camera may determine depth motion of an object by emitting light pulses, receiving reflected light pulses from the object, and accumulating a plurality of charges based on the reflected light pulses. The depth motion may be determined by the controller through analysis of the accumulated charges.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of co-pending and commonly ownedU.S. Provisional Pat. Application No. 62/714,900 entitled “DEPTH MOTIONDETERMINATION VIA TIME-OF-FLIGHT CAMERA” filed on Aug. 6, 2018, theentirety of which is hereby incorporated by reference.

TECHNICAL FIELD

The present embodiments relate generally to image sensors, andspecifically to depth motion determination via time-of-flight cameras.

BACKGROUND OF RELATED ART

Image sensors are often used to collect information and generate stilland/or moving images. Image sensors can be found in devices such asdigital cameras, video recorders, cell phones, and the like.

Lateral motion and depth motion may be detected by the image sensors.Lateral motion of an object may be motion in a plane parallel to theimage sensor. Depth motion of an object may be motion in a plane that isperpendicular to the image sensor. Lateral motion may be detected using2D imaging algorithms, such as optical flow algorithms. Some imagesensors, such as 3D cameras, may provide depth information (the distanceassociated with each pixel) in addition to 2D image information. Forthese 3D cameras, conventional methods of detecting depth motion (motiontoward or away from the image sensor) based on successive 3D images hasbeen slow and relatively inaccurate.

SUMMARY

This Summary is provided to introduce in a simplified form a selectionof concepts that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tolimit the scope of the claimed subject matter.

An apparatus is disclosed. The apparatus includes a light emitterconfigured to emit one or more light pulses, a photodetector configuredto detect reflections of the one or more light pulses and generate areflected light signal based on the detected reflections, a plurality ofcharge storage elements configured to accumulate charge based on thereflected light signal, and a controller. The controller executesinstructions stored in a memory that cause the apparatus to measure afirst plurality of accumulated charges associated with the first lightpulse, and determine a first phase-shift of the reflected light signalbased on the first plurality of accumulated charges, wherein the firstphase-shift indicates a depth motion of an object reflecting the firstlight pulse.

A method is disclosed. The method includes emitting, by a light emitter,one or more light pulses, detecting, by a photodetector, reflections ofthe one or more light pulses and generating a reflected light signalbased on the detected reflections, and accumulating charge, by aplurality of charge storage elements, based on the reflected lightsignal. The method further includes measuring a first plurality ofaccumulated charges associated with a first light pulse, and determininga first phase-shift of the reflected light signal based on the firstplurality of accumulated charges, wherein the first phase-shiftindicates a depth motion of an object reflecting the first light pulse.

An apparatus is disclosed. The apparatus includes a means for emittingone or more light pulses, a means for detecting reflections of the oneor more light pulses, and a means for generating a reflected lightsignal based on the detected reflections. The apparatus also includes ameans for accumulating charge, by a plurality of charge storageelements, based on the reflected light signal, a means for measuring aplurality of accumulated charges associated with a first light pulse,and a means determining a phase-shift of the reflected light signalbased on the plurality of accumulated charges, wherein the phase-shiftindicates a depth motion of an object reflecting the first light pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

The present embodiments are illustrated by way of example and are notintended to be limited by the figures of the accompanying drawings.

FIG. 1 shows a simplified diagram of an example time-of-flight camera.

FIG. 2 shows a simplified signal diagram depicting example waveformsassociated with light transmitted from, and received by, thetime-of-flight camera of FIG. 1 in the presence of motion.

FIG. 3 shows an example diagram of signals and charges that may beassociated with the time-of-flight camera of FIG. 1 .

FIG. 4 shows another example diagram of signals and charges that may beassociated with the time-of-flight camera of FIG. 1 .

FIG. 5 shows another example diagram of signals and stored charges thatmay be associated with the time-of-flight camera of FIG. 1 .

FIG. 6 is an illustrative flow chart depicting an example operation fordetermining a depth motion of an object, in accordance with someembodiments.

FIG. 7 shows a block diagram of an example time-of-flight camera.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forthsuch as examples of specific components, circuits, and processes toprovide a thorough understanding of the present disclosure. The term“coupled” as used herein means connected directly to or connectedthrough one or more intervening components or circuits. Also, in thefollowing description and for purposes of explanation, specificnomenclature is set forth to provide a thorough understanding of theaspects of the disclosure. However, it will be apparent to one skilledin the art that these specific details may not be required to practicethe example embodiments. In other instances, well-known circuits anddevices are shown in block diagram form to avoid obscuring the presentdisclosure. Some portions of the detailed descriptions which follow arepresented in terms of procedures, logic blocks, processing and othersymbolic representations of operations on data bits within a computermemory. The interconnection between circuit elements or software blocksmay be shown as buses or as single signal lines. Each of the buses mayalternatively be a single signal line, and each of the single signallines may alternatively be buses, and a single line or bus may representany one or more of a myriad of physical or logical mechanisms forcommunication between components.

Unless specifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present application,discussions utilizing the terms such as “accessing,” “receiving,”“sending,” “using,” “selecting,” “determining,” “normalizing,”“multiplying,” “averaging,” “monitoring,” “comparing,” “applying,”“updating,” “measuring,” “deriving” or the like, refer to the actionsand processes of a computer system, or similar electronic computingdevice, that manipulates and transforms data represented as physical(electronic) quantities within the computer system’s registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof, unless specificallydescribed as being implemented in a specific manner. Any featuresdescribed as modules or components may also be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a non-transitory computer-readable storagemedium comprising instructions that, when executed, performs one or moreof the methods described above. The non-transitory computer-readablestorage medium may form part of a computer program product, which mayinclude packaging materials.

The non-transitory processor-readable storage medium may comprise randomaccess memory (RAM) such as synchronous dynamic random access memory(SDRAM), read only memory (ROM), non-volatile random access memory(NVRAM), electrically erasable programmable read-only memory (EEPROM),FLASH memory, other known storage media, and the like. The techniquesadditionally, or alternatively, may be realized at least in part by aprocessor-readable communication medium that carries or communicatescode in the form of instructions or data structures and that can beaccessed, read, and/or executed by a computer or other processor.

The various illustrative logical blocks, modules, circuits andinstructions described in connection with the embodiments disclosedherein may be executed by one or more processors. The term “processor,”as used herein may refer to any general-purpose processor, conventionalprocessor, controller, microcontroller, and/or state machine capable ofexecuting scripts or instructions of one or more software programsstored in memory.

FIG. 1 shows a simplified diagram of an example time-of-flight (TOF)camera 100. The TOF camera 100 may detect points or objects in a sensingarea by emitting (transmitting) pulses of light that illuminate thepoints or objects and detecting reflected light pulses. The TOF camera100 may determine the distance to an object in the sensing area based ona delay between the time a light pulse is transmitted and the time acorresponding reflected light pulse is received from the object. Thisdelay time, which may also be referred to as a “time-of-flight” or around-trip time of the light pulse, may be multiplied by the speed oflight to determine the distance between the TOF camera 100 and anobject. In some example implementations, the TOF camera 100 may alsodetermine motion (depth motion) information associated with objectsbased on the time-of-flight information.

The TOF camera 100 is shown to include a number of light emitters 120, anumber of photodetectors 130, and a controller 140. The light emitters120 are coupled to the controller 140. The controller 140 may direct thelight emitters 120 to transmit or emit light toward an object 150 withinthe sensing area. In some implementations, the controller 140 maygenerate an emitter control signal 125 to cause the light emitters 120to emit one or more light pulses that may be used to detect the object150. The light emitters 120 may include any number of light sources suchas, for example, laser diodes, light emitting diodes (LEDs), verticalcavity surface emitting lasers (VCSEL), or any other suitable deviceconfigured to selectively transmit or emit light, including devices toemit light pulses at a source wavelength. The source wavelength mayinclude, for example, ultraviolet, visible, and/or infrared portions ofthe electromagnetic spectrum.

Transmitted light 170 emitted from the light emitters 120 may bereflected by the object 150 to generate reflected light 175 that may bereceived by the photodetectors 130. The photodetectors 130 may beconfigured to convert the reflected light 175 into electrical signalssuch as a reflected light signal 135, based on an intensity level of thereflected light 175. The photodetectors 130 may be any suitablecomponent or device that can receive or sense light including, forexample, photodiodes, avalanche photodiodes, phototransistors, pixelsensors, charge coupled devices (CCD), or the like.

The photodetectors 130 may be coupled to the controller 140. Thecontroller 140 may include analog and/or digital processing circuits forreceiving, converting, and processing signals from the photodetectors130. For example, in some implementations, the controller 140 mayinclude a plurality of capacitors 145 to accumulate charge based onsignals from the photodetectors 130. In other implementations thecapacitors 145 may be separate from the controller 140, yet still withinthe TOF camera 100. Other analog and/or digital processing circuits ofthe controller 140 are not shown for simplicity. The controller 140 maydetermine distances and motion associated with the object 150 based atleast in part on the TOF information associated with the emitter controlsignal 125 and the reflected light signal 135.

In some implementations, when the object 150 is in motion, an image ofthe object 150 (e.g., a frame of pixels captured through thephotodetectors 130) may be affected by motion artifacts. The motionartifacts may be undesirable and, in some cases, may blur or reduce thequality of the image. However, since the controller 140 can determinemotion information, the controller 140 may remove some or all of themotion artifacts from the image of the object 150 using well-knownmethods. In some aspects, the more detailed the determined motioninformation, the better the controller 140 can correct the image of theobject 150.

FIG. 2 shows a simplified timing diagram 200 depicting example waveformsassociated with light transmitted from, and received by, the TOF camera100 of FIG. 1 in the presence of depth motion. Depth motion may refer tomotion that is perpendicular to (toward or away from) the TOF camera. Incontrast, regular or lateral motion may refer to motion that isgenerally parallel to the TOF camera. In some implementations, acontroller, such as the controller 140 of FIG. 1 , may control lightemitters, such as the light emitters 120 from FIG. 1 , to generate oneor more transmitted light pulses by an emitter control signal 210. Theemitter control signal 210, and therefore the corresponding transmittedlight pulses, may be periodic. The example emitter control signal 210 isshown as having a period of 2π, however other periods are possible.

The light pulses corresponding to the emitter control signal 210 may bereflected by an object in the sensing area and received byphotodetectors, such as the photodetectors 130 of FIG. 1 . Thephotodetectors may generate a reflected light signal 220. As shown, thereflected light signal 220 may have a period corresponding to the periodof the emitter control signal 210. The reflected light signal 220 mayhave a baseline component B (e.g., an offset from an arbitraryreference) and an amplitude A. The baseline component B may be caused bybackground light washing over the foreground or object, independentlight sources adding light to the scene, or other sources. In addition,the received signal also may include noise.

In some example implementations, the photodetectors and/or thecontroller may accumulate and measure charge (e.g., an electric charge)associated with the reflected light signal 220. For example, the emittercontrol signal 210 may be divided into time periods, each π/2 long. Thetime periods may be used to determine the accumulated charge values. Inone example implementation, an amount of charge 230 may be associatedwith the reflected light signal 220 between the time period from 0 to π.Other amounts of charge associated with other time periods are possibleand are not shown for simplicity. The charges may be stored(accumulated) in a capacitor or other suitable charge storing element ordevice (not shown for simplicity) associated with the photodetectors.The reflected light signal 220 may be received at the TOF camera after adelay 240. The delay 240 may correspond to a TOF delay associated withthe propagation and reflection of light.

In some example implementations, the timing of the emitter controlsignal 210, the reflected light signal 220, and/or one or more charges230 associated with the reflected light signal 220 may be used todetermine distance and motion information associated with one or moreobjects in the sensing area. The motion information may include depthmotion information. Example procedures to determine motion associatedwith one or more objects are discussed in conjunction with FIGS. 3-6below.

FIG. 3 shows an example timing diagram 300 of signals and electriccharges that may be associated with the TOF camera 100 of FIG. 1 .Waveform 310 may show example timing information associated with theemitter control signal 125 of FIG. 1 during a burst duration P. Theburst duration P shown in FIG. 3 may be a duration of 4π. However, otherdurations are possible. Further, a burst duration P may include anyfeasible integer number of pulses. The waveform 310 is shown as aperiodic signal (period = 2π) and is plotted against equal (andarbitrary) time periods of π/2 duration. In other implementations, othertime periods are possible. For example, longer time periods (> π/2) orshorter time periods (< π/2) may be used. The waveform 310 may showtiming information corresponding to a periodic transmission of lightpulses.

Waveform 320 may show example timing and amplitude informationassociated with the reflected light signal 135 of FIG. 1 . In someimplementations, the baseline component B may be removed from thereflected light signal 135 (and the waveform 320). Persons having skillin the art will appreciate that there are a variety of processingprocedures available to remove the baseline component B from thereflected light signal 135. For example, signals may be received fromthe photodetectors 130 of FIG. 1 when the light emitters 120 are nottransmitting light. Such signals may be considered to be the baselinecomponent B that may be subtracted from subsequent signals received fromthe photodetectors 130 in response to light being transmitted from thelight emitters 120.

As shown, the waveform 320 may be delayed by a time period 360 withrespect to the waveform 310. In some example implementations, the timeperiod 360 may be referred to as a phase φ, or a phase delay. The phaseφ may refer to the difference between the phase of a transmit signal(e.g., the waveform 310) and the phase of a received signal (e.g., thewaveform 320). The time period 360 may be associated with a TOF delaydue to the distance between the TOF camera and an object, and thevelocity of light. If the object is in motion, then the TOF delay maynot be constant for a set of successive periods of the reflected lightsignal 135 shown in the waveform 320. In the timing diagram 300, the TOFdelay is shown to increase by a time, referred to as a phase-shift θ,for each time period π. Thus, time period 361 is φ+θ, time period 362 isφ+2θ, and time period 363 is φ+3θ in duration. In some implementations,the value of the phase-shift θ may also indicate relative motion withrespect to the TOF camera. For example, if the phase-shift θ ispositive, then the object reflecting light may be moving away from theTOF camera. In another example, if the phase-shift θ negative, then theobject reflecting light may be moving toward the TOF camera. In someother implementations, the relationship between the sign of thephase-shift θ and the direction of motion of the object may be reversed.(ln this example, motion is assumed to have a constant speed, which maybe true for small time periods θ with respect to the time period 2π. Inother words, the speed of the motion may be assumed to be constant whenthe duration of the light pulses is relatively small with respect to thespeed of the motion. The duration of the light pulses may be a fewmilliseconds. Thus, the speed of the motion may be constant orrelatively constant within the time of the duration of the lightpulses.) In other implementations, the TOF delay may decrease insubsequent time periods. The distance between the object and the TOFcamera may be associated with the phase (φand motion associated with theobject may be associated with the phase-shift θ.

Electric charge (sometimes referred to as “charge”, for simplicity) maybe accumulated (stored) based on the waveform 320 (e.g., the reflectedlight signal 135) and time periods referenced to the waveform 310 (e.g.,the emitter control signal 125). A different charge amount may beaccumulated for different time periods. In some example implementations,the number of accumulated charges may be related to time periodsassociated with the waveform 320.

The waveform 310 shows a first accumulated charge

Q̂₀

that may be associated with a time period 0 to π. Waveform 330 shows asecond accumulated charge

${\hat{\, Q}}_{1}$

that may be associated with a time period π/2 to 3π/2. Waveform 340shows a third accumulated charge

${\hat{\, Q}}_{2}$

that may be associated with a time period π to 2π. Finally, signal 350shows a fourth accumulated charge

 Q̂₃

that may be associated with a time period 3π/2 to 5π/2. Note thataccumulated charges

${\hat{Q}}_{0},{\hat{\, Q}}_{1},{\hat{\, Q}}_{2},\,\,{\hat{Q}}_{3}$

are also associated with the waveform 320 (e.g., the reflected pulses220 without the baseline component B).

In other words, the waveform 310, which is associated with transmittedlight pulses, and the waveform 320, which is associated with thereflected light pulses minus the offset B, may control directly orindirectly, accumulation of charge

Q̂₀.

The waveforms 330, 340, and 350 may be time-shifted versions of thewaveform 310. The waveform 330 is shifted by π/2 with respect to thewaveform 310 may control the accumulation of charge

${\hat{\, Q}}_{1}.$

The waveform 340 is shifted by π with respect to the waveform 310 andmay control accumulation of charge

${\hat{\, Q}}_{2}.$

The waveform 350 is shifted by 3π/2 with respect to the waveform 310 andmay control accumulation of charge

 Q̂₃.

In some example implementations, accumulation of charge may occur when afirst signal (e.g., waveform 310, 330, 340, or 350) is a logical “1” anda second signal (e.g., waveform 320) is also a logical 1 during a timeperiod referenced to the first signal. The time periods associated witheach first signal may be as discussed above. That is, the time periodfor waveform 310 is 0 to π, the time period for the waveform 330 is π/2to 3π/2, the time period for the waveform 340 is π to 2π, and the timeperiod for the waveform 350 is 3π/2 to 5π/2.

The accumulated charges

${\hat{Q}}_{0},{\hat{\, Q}}_{1},{\hat{\, Q}}_{2},\,\,{\hat{Q}}_{3}$

may be expressed by the set of equations below:

$\begin{matrix}\left\{ \begin{array}{l}{{\hat{Q}}_{0} = A\left( {\pi - \varphi - \left( {N - 1} \right)\theta} \right)} \\{{\hat{Q}}_{1} = A\left( {{\pi/2} + \varphi + N\theta} \right)} \\{{\hat{Q}}_{2} = A\left( {\varphi + N\theta} \right)} \\{{\hat{Q}}_{3} = A\left( {{\pi/2} - \varphi - \left( {N - 1} \right)\theta} \right)}\end{array} \right) & \text{­­­[eq. 1]}\end{matrix}$

where A is the amplitude of the waveform 320;

-   N is a total number of excitation pulses within a burst duration-   φ is the phase associated with the waveform 320; and-   θ is the phase-shift associated with the waveform 320.

The total number of excitation pulses may refer to a number ofexcitation pulses within a burst duration. The example of FIG. 3 shows aburst duration P having a first excitation pulse N and a secondexcitation pulse N+1. Note that in this example, the second excitationpulse N+1 is successive and/or adjacent to the first excitation pulse N.Although only two excitation pulses are shown here, any number ofexcitation pulses are possible. As noted above, the accumulated charges

Q̂₀, Q̂₁, Q̂₂, Q̂₃

of equation 1 may be associated with a reflected light signal minus abaseline component.

After a burst of N excitation pulses, the accumulated charges may bemeasured, digitized, and used to determine the phase φ (distance) and/orthe phase-shift θ (depth motion) thereby providing distance and motioninformation, respectively, of a detected object. In someimplementations, an analog-to-digital converter (ADC) may be used tomeasure the accumulated charges. In other implementations, other methodsmay be used. For example, a timer may be controlled by the emittercontrol signal and the reflected light signal to determine anaccumulated charge based on the timer values. Persons skilled in the artwill recognize that other feasible techniques are possible. One examplesolution for determining the phase φ and the phase-shift θ based onaccumulated charges of equation 1 is expressed in the equations below:

$\begin{matrix}{\varphi = \frac{\pi}{2}\frac{N{\hat{Q}}_{0} - \left( {3N - 2} \right){\hat{Q}}_{2} + N{\hat{Q}}_{1} - 3N{\hat{Q}}_{3}}{\left( {{\hat{Q}}_{0} - {\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} - {\hat{Q}}_{3}} \right)}} & \text{­­­[eq.2]}\end{matrix}$

$\begin{matrix}{\theta = - \frac{\pi}{2}\frac{\left( {{\hat{Q}}_{0} - 3{\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} - 3{\hat{Q}}_{3}} \right)}{\left( {{\hat{Q}}_{0} - {\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} + {\hat{Q}}_{3}} \right)}} & \text{­­­[eq. 3]}\end{matrix}$

Note that the system of equations in equation 1 includes four equationsin three unknowns. Thus, solution shown in equations 2, and 3 may be oneof many possible solutions.

In some example implementations, the solution for the linear system ofequations shown in equation 1 may be found using a least mean square(LMS) approach. For example, the system of equations expressed inequation 1 may be rearranged based on the equation below:

$\begin{matrix}{A = \frac{1}{\pi}\left\lbrack {\left( {{\hat{Q}}_{0} - {\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} - {\hat{Q}}_{3}} \right)} \right\rbrack} & \text{­­­[eq.4]}\end{matrix}$

Substituting equation 4 into equation 1 and then solving to minimize amean square error yields a solution for phase-shift θ expressed by theequation below:

$\begin{matrix}{\theta = - \frac{\pi}{2}\frac{\left( {{\hat{Q}}_{0} - 3{\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} - 3{\hat{Q}}_{3}} \right)}{\left( {{\hat{Q}}_{0} - {\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} + {\hat{Q}}_{3}} \right)}} & \text{­­­[eq. 5]}\end{matrix}$

Thus, a least mean square approach may yield a similar solution for thephase-shift θ (shown in equation 5) as shown earlier in equation 3. Insome example implementations, the phase-shift θ may be proportional tothe depth motion of the object during the burst duration. As describedabove, motion of the selected object (e.g., speed of the object) isassumed to be constant. In some example implementations, if the motionof the object is not constant, then the phase-shift θ may represent anaverage phase-shift. Notably, the phase-shift θ may be determined with asingle light pulse. In other words, both a distance φ and a depth motionθ may be determined with each pulse of light. Thus, the solutionexpressed in equation 5 may determine depth motion more quickly thanother methods which may rely on multiple pulses to provide multipledistance measurements with which to determine depth motion.

The solutions for the phase-shift θ described in equations 3 and 5 arebased on a removal of the offset B from the reflected light signal 135.In some other example implementations, the offset B may be removed fromsolution computations by generating the light pulses with an asymmetricform factor (or a duty cycle that is other than 50%). One example ofusing non-symmetric form factor light pulses is described below inconjunction with FIG. 4 .

FIG. 4 shows another example timing diagram 400 of signals and chargesthat may be associated with the TOF camera 100 of FIG. 1 . Waveform 410may show example timing information associated with the emitter controlsignal 125 of FIG. 1 . Although, the waveform 410 is shown as a periodicsignal with a period of 2π, the form factor of waveform 410 isnon-symmetric. The non-symmetric form factor of the waveform 410 may bedifferent from the symmetric form factor of the waveform 310 of FIG. 3 .As shown, the waveform 410 is high (e.g., the light emitters 120 of FIG.1 are emitting light) between the times 0 to π+Δ where Δ is a constant.Similarly, the waveform 410 is low (e.g., the light emitters 120 are notemitting light) between the times π +Δ and 2π. The waveform 410 is shownplotted against equal time periods of π/2 duration. Waveform 420 mayshow example timing and amplitude information associated with thereflected light signal 135. Although not shown for simplicity, thewaveform 420 may include a baseline component B in addition to a signalamplitude A, for example, as described with respect to FIG. 2 .

As shown, the waveform 420 is delayed by a time 460 (phase φ) withrespect to the waveform 410. The time 460 may correspond to a TOF delaydue to the distance between the TOF camera 100 and an object, and thevelocity of light. If the object is in motion, then the TOF delay maynot be constant. In the timing diagram 400, the TOF delay is shown toincrease by εθ for each time period π+Δ (for example, see time 461). Inother example, the TOF delay may decrease in successive time periods asthe TOF delay is associated with the direction of the object withrespect to the TOF camera 100. Similar to the timing diagram 300 of FIG.3 , the distance between the object and the TOF camera 100 may berepresented by a phase φ and motion associated with the object may berepresented by a phase-shift θ.

Charge may be accumulated (stored) based on the waveform 420 (e.g., thereflected light signal 135) during time periods referenced to thewaveform 410 (e.g., the emitter control signal 125). A different chargeamount may be accumulated for different time periods. In some exampleimplementations, the number of charges accumulated may be related to anumber of time periods associated with waveform 410.

The waveform 410 shows a first accumulated charge Q₀ that may beassociated with a time period 0 to (π+Δ). Waveform 430 shows a secondaccumulated charge Q₁ that may be associated with a time period π/2 to(2π-Δ). Waveform 440 shows a third charge Q₂that may be associated witha time period (π+Δ) to 2π. Finally, waveform 450 shows a fourth chargeQ₃ that may be associated with a time period 3π/2 to (3π-Δ). Note thatthe ε is constant related to a pulse wave form factor (sometimesreferred to as duty cycle) of the waveform 410 and is expressed by theequation below:

$\begin{matrix}{\varepsilon = \frac{\pi + \text{Δ}}{2\pi} = const} & \text{­­­[eq. 6]}\end{matrix}$

The accumulated charges Q₀-Q₃ may be expressed by the set of equationsbelow:

$\begin{matrix}\left\{ \begin{array}{l}{Q_{0} = \frac{1}{N}{\sum_{i = 0}^{N - 1}\left\lbrack {B + A\left( {\left( {\pi + \text{Δ}} \right) - \varphi - i\theta} \right)} \right\rbrack}} \\{Q_{1} = \frac{1}{N}{\sum_{i = 0}^{N - 1}\left\lbrack {B + A\left( {\left( {\pi + \text{Δ}} \right) - \frac{\pi}{2} + \varphi + \left( {i + \varepsilon} \right)\theta} \right)} \right\rbrack}} \\{Q_{2} = \frac{1}{N}{\sum_{i = 0}^{N - 1}\left\lbrack {B + A\left( {2\text{Δ} + \varepsilon\theta} \right)} \right\rbrack}} \\{Q_{3} = \frac{1}{N}{\sum_{i = 0}^{N - 1}\left\lbrack {B + A\left( {\frac{3\pi}{2} - \left( {\pi - \text{Δ}} \right) - \varphi - i\theta} \right)} \right\rbrack}}\end{array} \right) & \text{­­­[eq. 7]}\end{matrix}$

Solving equation 7 for the phase-shift θ yields the equation below:

$\begin{matrix}{\theta = \frac{\pi}{4\varepsilon}\frac{15Q_{01} - 9Q_{02} - 11Q_{13} + 17Q_{23}}{Q_{01} + Q_{23} + Q_{02} + Q_{13}} - 4\pi\frac{Q_{01} - Q_{02} - Q_{13} + Q_{23}}{Q_{01} + Q_{23} + Q_{02} + Q_{13}}} & \text{­­­[eq. 8]}\end{matrix}$

As discussed above, the phase-shift θ may be proportional to the motion,such as a depth motion, of a detected object. Equation 8 makes use of anotation related to a difference between accumulated charges,hereinafter referred to a differential accumulated charge. In oneexample implementation, the differential accumulated charges may beexpressed by the equation set below:

$\begin{matrix}\left\{ \begin{array}{l}{Q_{01} \triangleq Q_{0} - Q_{1} = - A\left( {2\varphi + \left( {N - 1 + \varepsilon} \right)\theta - \frac{\pi}{2}} \right)} \\{Q_{23} \triangleq Q_{2} - Q_{3} = + A\left( {\varphi + \left( {\frac{N - 1}{2} + \varepsilon} \right)\theta + 2\pi\varepsilon - \frac{3\pi}{2}} \right)} \\{Q_{02} \triangleq Q_{0} - Q_{2} = - A\left( {\varphi + \left( {\frac{N - 1}{2} + \varepsilon} \right)\theta + 2\pi\varepsilon - 2\pi} \right)} \\{Q_{13} \triangleq Q_{1} - Q_{3} = + A\left( {2\varphi + \left( {N - 1 + \varepsilon} \right)\theta} \right)}\end{array} \right) & \text{­­­[eq. 9]}\end{matrix}$

Note that in the differential accumulated charge equations above, thebaseline component B has been canceled out, and therefore not requiredin determining the solution for the phase-shift θ. Similar to equation 5above, the phase-shift θ in equation 8 may be determined with a singlelight pulse.

In some example implementations, changing the definitions of thedifferential accumulated charges may provide a different solution forthe phase-shift θ. That is, a different solution for the phase-shift θmay be obtained using different differential accumulated charge values.

For example, the charge differences may be defined as expressed below:

$\begin{matrix}\begin{array}{l}{Q_{01} \triangleq Q_{0} - Q_{1} = - A\left( {2\varphi + \left( {N - 1 + \varepsilon} \right)\theta - \frac{\pi}{2}} \right)} \\{Q_{12} \triangleq Q_{1} - Q_{2} = + A\left( {\varphi + \frac{N - 1}{2}\theta - 2\pi\varepsilon + \frac{3\pi}{2}} \right)} \\{Q_{23} \triangleq Q_{2} - Q_{3} = + A\left( {\varphi + \left( {\frac{N - 1}{2} + \varepsilon} \right)\theta + 2\pi\varepsilon - \frac{3\pi}{2}} \right)} \\{Q_{30} \triangleq Q_{3} - Q_{0} = - A\left( \frac{\pi}{2} \right)}\end{array} & \text{­­­[eq. 10]}\end{matrix}$

Returning to equation 7 and solving for the phase-shift θ using equation10:

$\begin{matrix}{\theta = \frac{\pi}{2\varepsilon}\frac{\left( {6 - 8\varepsilon} \right)Q_{30} + Q_{12} - Q_{23}}{Q_{30}}} & \text{­­­(eq. 11)}\end{matrix}$

Although the duty cycle of the waveforms shown in FIG. 4 is greater than50%, in other implementations, the duty cycle may be less than 50% andthe solutions outlined in equations 6 through 11 would still beapplicable.

In other example implementations, the light pulses emitted by the lightemitter may be pulsed periodically during a frame time. One such exampleimplementation is discussed below in conjunction with FIG. 5 .

FIG. 5 shows another example timing diagram 500 of signals and chargesthat may be associated with the TOF camera 100 of FIG. 1 . Waveform 510may show example timing information associated with the emitter controlsignal 125 of FIG. 1 . The example timing diagram 500 shows the waveform510 as including four bursts (Burst₀ - Burst₃) for simplicity. In otherimplementations, the waveform 510 may include any feasible number ofbursts.

Signal 520 may show example timing and amplitude information associatedwith the reflected light signal 135 based on the light bursts depictedin the waveform 510. As shown, the signal 520 is delayed with respect tothe waveform 510. Although not shown, the signal 520 may include anamplitude A and a baseline component B. The delay may be associated witha TOF delay due to the distance between the TOF camera 100 and anobject, and the velocity of light. If the object is in motion, the TOFdelay may not be constant.

Charge may be accumulated based on the signal 520 (e.g., the reflectedlight signal 135) during time periods referenced to the waveform 510(e.g., the emitter control signal 125). For example, waveform 515 mayshow timing and amplitude information associated with the lightreflected from the first burst (Burst₀). In some implementations, theremay be no discernible phase-shift between the waveform 510 and thewaveform 515. A first charge Q₀ (not shown for simplicity) may beaccumulated based on the waveform 515. Waveform 530 may have a π/2phase-shift with respect to the waveform 510, and may show timing andamplitude information associated with light reflected from the secondburst (Burst₁). A second charge Q₁ (not shown for simplicity) may beaccumulated based on the waveform 530. Similarly, waveform 540, may havea π phase-shift with respect to the waveform 510, and may show timingand amplitude information associated with light reflected from the thirdburst (Burst₂). A third charge Q₂ (not shown for simplicity) may beaccumulated based on the waveform 540. Waveform 550 may have a 3π/2phase-shift with respect to the waveform 510, and may show timing andamplitude information associated with light reflected from the fourthburst (Bursts). A fourth charge Q₃ (not shown for simplicity) may beaccumulated based on the waveform 550. The accumulated charges may beexpressed by the equations below:

$\begin{matrix}\left\{ \begin{array}{l}{Q_{0} = B + A\left( {\pi - \varphi + 1.5\theta} \right)} \\{Q_{1} = B + A\left( {\frac{\pi}{2} + \varphi - 0.5\theta} \right)} \\{Q_{2} = B + A\left( {\varphi + 0.5\theta} \right)} \\{Q_{3} = B + A\left( {\frac{\pi}{2} - \varphi - 1.5\theta} \right)}\end{array} \right) & \text{­­­(eq. 12)}\end{matrix}$

The phase-shift θ may be expressed by the equation below:

$\begin{matrix}{\theta = \frac{\pi}{2}\frac{- Q_{01}Q_{13} + 2Q_{01}Q_{23} - Q_{02}Q_{23}}{3Q_{01}Q_{13} - 4Q_{02}Q_{13} - 2Q_{01}Q_{23} + 3Q_{02}Q_{23}}} & \text{­­­(eq. 13)}\end{matrix}$

In another example implementation, if no baseline component B is presentin the signal 520 (e.g., if the baseline component B is removed asdescribed above with respect to FIG. 3 ), then the equation (12) may bewritten as:

$\begin{matrix}\left\{ \begin{array}{l}{Q_{0} = A\left( {\pi - \varphi + 1.5\theta} \right)} \\{Q_{1} = A\left( {\frac{\pi}{2} + \varphi - 0.5\theta} \right)} \\{Q_{2} = A\left( {\varphi + 0.5\theta} \right)} \\{Q_{3} = A\left( {\frac{\pi}{2} - \varphi - 1.5\theta} \right)}\end{array} \right) & \text{­­­(eq. 14)}\end{matrix}$

Equation 14 may be solved for the phase-shift θ to determine depthmotion as expressed below:

$\begin{matrix}{\theta = \frac{\pi}{2}\frac{Q_{0} - Q_{1} + Q_{2} - Q_{3}}{Q_{0} + Q_{1} + Q_{2} + Q_{3}}} & \text{­­­(eq. 15)}\end{matrix}$

FIG. 6 is an illustrative flow chart depicting an example operation 600for determining a depth motion of an object, in accordance with someembodiments. By way of example, the operation 600 may be performed bythe controller 140 of FIG. 1 . In other embodiments, the operation 600may be performed by a processor (including a general-purpose processor),a state machine or any other technically feasible device. In someembodiments, the operation 600 may include fewer or more operationalsteps than those depicted in the example of FIG. 6 . Further, two ormore of the operational steps may be performed in a different orderand/or in parallel.

The controller 140 first causes pulses of light to be emitted by one ormore light emitters toward a sensing area (602). In someimplementations, the controller 140 may control the light emittersthrough an emitter control signal. In some implementations, thecontroller 140 may cause the one or more light emitters to emit a burstof light pulses. Next, the controller 140 detects reflected lightthrough one or more photodetectors (604). In some implementations, thecontroller may detect reflected light by receiving a reflected lightsignal from the one or more photodetectors.

Next, the controller 140 accumulates charges based on the detectedreflected light (606). In some implementations, charge may beaccumulated based, at least in part, on timing and amplitude informationincluded in the reflected light signal. For example, as described abovewith respect to FIGS. 3-5 , the charges may be accumulated based on acomparison of the reflected light signal and a version of the emittercontrol signal. In some embodiments, charges may be accumulated in aplurality of capacitors.

Next, the controller 140 measures the accumulated charges (608). In someimplementations, the controller 140 may digitize and measure theaccumulated charges. For example, the controller 140 may cause an ADC todetermine the amount of charge stored in the capacitors duringoperational step 606.

Next, the controller 140 determines depth motion based on the measuredaccumulated charges (610). As described above with respect to FIGS. 3-5, the controller 140 can determine motion, including depth motion bydetermining a phase-shift based on the measured accumulated charges. Insome implementations, differential accumulated charge may also be usedto determine depth motion.

FIG. 7 shows a block diagram of an example TOF camera 700. The TOFcamera 700 may be one implementation of the TOF camera 100 of FIG. 1 ,and may include light emitters 710, photodetectors 720, a processor 730,and a memory 740. The light emitters 710 and the photodetectors 720 maybe implementations of the light emitters 120 and the photodetectors 130of FIG. 1 .

The light emitters 710 may be coupled to the processor 730. Theprocessor 730 may cause the light emitters 710 to emit a plurality oflight pulses toward the sensing area. In one example implementation, theprocessor 730 may control the light emitters 710 with an emitter controlsignal 715. The photodetectors 720 may also be coupled to the processor730. The photodetectors 720 may receive reflected light pulses from thesensing area and generate a related reflected light signal 725.

The memory 740 may include a non-transitory computer-readable medium(e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM,Flash memory, a hard drive, etc.) that may store at least the followingsoftware (SW) modules:

-   a light emitter control SW module 742 to control the operation    (e.g., turning on and off) of the light emitters 610;-   a photodetector control SW module 744 to control the operation of    the photodetectors 720; and-   a motion detection SW module 746 to determine depth motion of an    object within the sensing area based on light transmitted by the    light emitters 710 and detected by the photodetectors 720.

Each software module includes instructions that, when executed by theprocessor 730, cause the TOF camera 700 to perform the correspondingfunctions. The non-transitory computer-readable medium of memory 740thus includes instructions for performing all or a portion of theoperations described above with respect to FIGS. 3-6 .

The processor 730 may execute the light emitter control SW module 742 togenerate the emitter control signal 715 causing the light emitters 710to emit a plurality of light pulses toward the sensing area. In someimplementations, execution of the light emitter control SW module 742may determine timing information associated with the emission of lightpulses and also cause the light emitters 710 to emit bursts of lightpulses.

The processor 730 may execute the photodetector control SW module 744 todetermine timing information associated with the reflected light signal725 provided by the photodetectors 720.

The processor 730 may execute the motion detection SW module 746 todetermine depth motion information. In some implementations, executionof the motion detection SW module 746 may determine accumulated chargeinformation associated with emitted and received light pulses. Inaddition, execution of the motion detection SW module 746 may determinecorresponding phase and phase-shift information. The phase informationmay be associated with the distance of objects from the TOF camera 700.Similarly, the phase-shift information may be associated with (and insome cases proportional to) the depth motion of objects within thesensing area. Thus, the motion detection SW module 746 may perform oneor more of the operations described in conjunction with FIGS. 3-6

Processor 730 may be any suitable one or more processors, controllers,state machines, FPGAs or the like, capable executing scripts orinstructions of one or more software programs stored in the TOF camera700 (e.g., within memory 740). For example, the processor 730 mayexecute the light emitter control SW module 742 to cause one or morepulses of light to be emitted toward a sensing area. The processor 730may also execute the photodetector control SW module 744 to receivelight reflected by an object within the sensing area. Further, theprocessor 730 may execute the motion detection SW module 746 todetermine TOF information associated with the transmitted and reflectedlight and determine accumulated charge information. In some exampleimplementations, the processor 730 may execute the motion detection SWmodule 746 to determine a phase and a phase-shift associated an object,and thereby determine a distance and a depth motion of the object.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the aspects disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the disclosure.

The methods, sequences or algorithms described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

In the foregoing specification, embodiments have been described withreference to specific examples thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader scope of the disclosure as set forth in theappended claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

The invention claimed is:
 1. An apparatus for determining a depth motionof an object, comprising: a light emitter configured to emit one or morelight pulses; a photodetector configured to detect reflections of theone or more light pulses and generate a reflected light signal based onthe detected reflections; a plurality of charge storage elementsconfigured to accumulate charge based on the reflected light signal; acontroller; and a memory storing instructions that, when executed by thecontroller, cause the apparatus to: measure a first plurality ofaccumulated charges associated with a first light pulse of the one ormore light pulses; and determine a first phase-shift of the reflectedlight signal based on the first plurality of accumulated chargesassociated with the first light pulse and without measuring accumulatedcharges associated with any other light pulses emitted by the lightemitter, wherein the first phase-shift indicates a motion of a firstobject toward or away from the photodetector, the first objectreflecting the first light pulse.
 2. The apparatus of claim 1, whereinthe instructions to determine the first phase-shift cause the apparatusto further: determine charge differences between two or more of thecharge storage elements, wherein the first phase-shift is determinedbased on the determined charge differences.
 3. The apparatus of claim 1,wherein execution of the instructions causes the apparatus to further:measure a second plurality of accumulated charges accumulated withrespect to the reflected light signal associated with a second lightpulse; and determine a second phase-shift of the reflected light signalbased on the second plurality of accumulated charges, wherein the secondphase-shift indicates a motion of a second object toward or away fromthe photodetector, the second object reflecting the second light pulse.4. The apparatus of claim 3, wherein the first and the second lightpulses are successive in sequence.
 5. The apparatus of claim 1, whereinthe first plurality of accumulated charges are determined with respectto a plurality of time periods based at least in part on timinginformation associated with the first light pulse.
 6. The apparatus ofclaim 5, wherein the first phase-shift is expressed by$\theta = - \frac{\pi}{2}\frac{\left( {{\hat{Q}}_{0} - 3{\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} - 3{\hat{Q}}_{3}} \right)}{\left( {{\hat{Q}}_{0} - {\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} + {\hat{Q}}_{3}} \right)},$where θ is the first phase-shift, and${\hat{Q}}_{0},{\hat{\, Q}}_{1},{\hat{\, Q}}_{2},\,\, and\,\,{\hat{Q}}_{3}$are four accumulated charges, and π is related to a period associatedwith the first light pulse.
 7. The apparatus of claim 1, wherein thefirst plurality of accumulated charges include charge due to backgroundlight, independent light sources, or a combination thereof.
 8. Theapparatus of claim 1, wherein the first light pulse has a non-symmetricform factor.
 9. The apparatus of claim 8, wherein the first phase-shiftis expressed by$\theta = \frac{\pi}{4\varepsilon}\frac{15Q_{01} - 9Q_{02} - 11Q_{13} + 17Q_{23}}{Q_{01} + Q_{23} + Q_{02} + Q_{13}} - 4\pi\frac{Q_{01} - Q_{02} - Q_{13} + Q_{23}}{Q_{01} + Q_{23} + Q_{02} + Q_{13}},$where θ is the first phase-shift, Q ₀₁ is a charge based on a differencebetween a first accumulated charge Q₀ and a second accumulated chargeQ₁, Q₀₂ is a charge based on a difference between the first accumulatedcharge Q₀ and a third accumulated charge Q₂, Q₁₃ is a charge based on adifference between the second accumulated charge Q₁ and a fourthaccumulated charge Q₃, Q₂₃ is a charge based on a difference between thethird accumulated charge Q₂ and the fourth accumulated charge Q₃, ε is aconstant based on the non-symmetric form factor, and π is related to aperiod of the first light pulse.
 10. The apparatus of claim 8, whereinthe first phase-shift is expressed by$\theta = \frac{\pi}{2\varepsilon}\frac{\left( {6 - 8\varepsilon} \right)Q_{30} + Q_{12} - Q_{23}}{Q_{30}},$where θ is the first phase-shift, Q ₃₀ is a charge based on a differencebetween a fourth accumulated charge Q₃ and a first accumulated chargeQ₀, Q₁₂ is a charge based on difference between a second accumulatedcharge Q₁ and a third accumulated charge Q₂, Q₂₃ is a charge based on adifference between the third accumulated charge Q₂ and the fourthaccumulated charge Q₃, ε is a constant based on the non-symmetric formfactor, and π is related to a period of the first light pulse.
 11. Amethod for determining a depth motion of an object from a reflectedlight signal, the method comprising: emitting, by a light emitter, oneor more light pulses; detecting, by a photodetector, reflections of theone or more light pulses and generating a reflected light signal basedon the detected reflections; accumulating charge, by a plurality ofcharge storage elements, based on the reflected light signal; measuringa first plurality of accumulated charges associated with a first lightpulse of the one or more light pulses; and determining a firstphase-shift of the reflected light signal based on the first pluralityof accumulated charges associated with the first light pulse and withoutmeasuring accumulated charges associated with any other light pulsesemitted by the light emitter, wherein the first phase-shift indicates amotion of a first object toward or away from the photodetector, thefirst object reflecting the first light pulse.
 12. The method of claim11, further comprising determining charge differences between two ormore of the charge storage elements, wherein the first phase-shift isdetermined based on the determined charge differences.
 13. The method ofclaim 11, further comprising: measuring a second plurality ofaccumulated charges accumulated with respect to the reflected lightsignal associated with a second light pulse reflected from the object;and determining a second phase-shift of the reflected light signal basedon the second plurality of accumulated charges, wherein the secondphase-shift indicates a motion of a second object toward or away fromthe photodetector, the second object reflecting the second light pulse.14. The method of claim 13, wherein the first and the second lightpulses are successive in sequence.
 15. The method of claim 11, whereinthe first plurality of accumulated charges are determined with respectto a plurality of time periods based at least in part on timinginformation associated with the first light pulse.
 16. The method ofclaim 15, wherein the first phase-shift is expressed by$\theta = - \frac{\pi}{2}\frac{\left( {{\hat{Q}}_{0} - 3{\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} - 3{\hat{Q}}_{3}} \right)}{\left( {{\hat{Q}}_{0} - {\hat{Q}}_{2}} \right) + \left( {{\hat{Q}}_{1} + {\hat{Q}}_{3}} \right)},$where θ is the first phase-shift, and${\hat{Q}}_{0},{\hat{\, Q}}_{1},{\hat{\, Q}}_{2},\,\, and\,\,{\hat{Q}}_{3}$are four accumulated charges, and π is related to a period associatedwith the first light pulse.
 17. The method of claim 11, wherein thefirst light pulse has a non-symmetric form factor and the firstphase-shift is expressed by$\theta = \frac{\pi}{4\varepsilon}\frac{15Q_{01} - 9Q_{02} - 11Q_{13} + 17Q_{23}}{Q_{01} + Q_{23} + Q_{02} + Q_{13}} - 4\pi\frac{Q_{01} - Q_{02} - Q_{13} + Q_{23}}{Q_{01} + Q_{23} + Q_{02} + Q_{13}},$where θ is the first phase-shift, Q ₀₁ is a charge based on a differencebetween a first accumulated charge Q₀ and a second accumulated chargeQ₁, Q₀₂ is a charge based on a difference between the first accumulatedcharge Q₀ and a third accumulated charge Q₂, Q₁₃ is a charge based on adifference between the second accumulated charge Q₁ and a fourthaccumulated charge Q₃, Q₂₃ is a charge based on a difference between thethird accumulated charge Q₂ and the fourth accumulated charge Q₃, ε is aconstant based on the non-symmetric form factor, and π is related to aperiod of the first light pulse.
 18. An apparatus comprising: means foremitting one or more light pulses; means for detecting reflections ofthe one or more light pulses; means for generating a reflected lightsignal based on the detected reflections; means for accumulating charge,by a plurality of charge storage elements, based on the reflected lightsignal; means for measuring a plurality of accumulated chargesassociated with a first light pulse of the one or more light pulses; andmeans for determining a phase-shift of the reflected light signal basedon the plurality of accumulated charges associated with the first lightpulse, and without measuring accumulated charges associated with anyother light pulses emitted by the light emitter, wherein the phase-shiftindicates a motion of an object toward or away from the means fordetecting the reflections of the one or more light pulses.